Application of the spiral vortex

Early  water turbines were designed to replace water mills that were used for grinding, fulling, crushing etc. They used the small differences in level in dammed rivers. Figure 15-11 shows the arrangement. The water entered the forebay and flowed into the ring of guide blades where a spiral vortex was formed. In this vortex pressure energy was changed to kinetic energy. The water leaving the guide blades then flowed through the rotating runner where the kinetic energy and the remaining pressure energy was transferred to the shaft to drive its load. The water then left through the draft tube. All the subsequent pressure turbines developed from this simple design. Clearly the spiral vortex, even if it only exists in the small space between the guides and the runner, is an essential feature of water turbines and we have sufficient information to size the components of the guide system. I shall come back to this when I deal with water turbines.